693 research outputs found
Cosmological Signature of Tachyon Condensation
We consider the dynamics of the open string tachyon condensation in a
framework of the cubic fermionic String Field Theory including a non-minimal
coupling with closed string massless modes, the graviton and the dilaton.
Coupling of the open string tachyon and the dilaton is motivated by the open
String Field Theory in a linear dilaton background and the flat space-time. We
note that the dilaton gravity provides several restrictions on the tachyon
condensation and show explicitly that the influence of the dilaton on the
tachyon condensation is essential and provides a significant effect:
oscillations of the Hubble parameter and the state parameter become of a
cosmological scale. We give an estimation for the period of these oscillations
(0.1-1) Gyr and note a good agreement of this period with the observed
oscillations with a period (0.15-0.65) Gyr in a distribution of quasar spectra.Comment: 19 pages, JHEP3 class; v2: presentation in Section 3 improve
Electrodynamics of Josephson vortex lattice in high-temperature superconductors
We studied response of the Josephson vortex lattice in layered
superconductors to the high-frequency c-axis electric field. We found a simple
relation connecting the dynamic dielectric constant with the perturbation of
the superconducting phase, induced by oscillating electric field. Numerically
solving equations for the oscillating phases, we computed the frequency
dependences of the loss function at different magnetic fields, including
regions of both dilute and dense Josephson vortex lattices. The overall
behavior is mainly determined by the c-axis and in-plane dissipation
parameters, which is inversely proportional to the anisotropy. The cases of
weak and strong dissipation are realized in
and underdoped correspondingly. The main feature of the response is the
Josephson-plasma-resonance peak. In the weak-dissipation case additional
satellites appear in the dilute regime mostly in the higher-frequency region
due to excitation of the plasma modes with the wave vectors set by the lattice
structure. In the dense-lattice limit the plasma peak moves to higher frequency
and its intensity rapidly decreases, in agreement with experiment and
analytical theory. Behavior of the loss function at low frequencies is well
described by the phenomenological theory of vortex oscillations. In the case of
very strong in-plane dissipation an additional peak in the loss function
appears below the plasma frequency. Such peak has been observed experimentally
in underdoped . It is caused by frequency
dependence of in-plane contribution to losses rather then a definite mode of
phase oscillations.Comment: 10 pages, 7 figures, to be published in Phys.Rev.B, supplementary
animations of oscillating local electric field can be found at
http://mti.msd.anl.gov/homepages/koshelev/projects/JPRinJVL/Nz2vc0_32vab6_0Anim.ht
inflation to probe non-perturbative quantum gravity
It is natural to expect a consistent inflationary model of the very early
Universe to be an effective theory of quantum gravity, at least at energies
much less than the Planck one. For the moment, , or shortly ,
inflation is the most successful in accounting for the latest CMB data from the
PLANCK satellite and other experiments. Moreover, recently it was shown to be
ultra-violet (UV) complete via an embedding into an analytic infinite
derivative (AID) non-local gravity. In this paper, we derive a most general
theory of gravity that contributes to perturbed linear equations of motion
around maximally symmetric space-times. We show that such a theory is quadratic
in the Ricci scalar and the Weyl tensor with AID operators along with the
Einstein-Hilbert term and possibly a cosmological constant. We explicitly
demonstrate that introduction of the Ricci tensor squared term is redundant.
Working in this quadratic AID gravity framework without a cosmological term we
prove that for a specified class of space homogeneous space-times, a space of
solutions to the equations of motion is identical to the space of backgrounds
in a local model. We further compute the full second order perturbed
action around any background belonging to that class. We proceed by extracting
the key inflationary parameters of our model such as a spectral index (),
a tensor-to-scalar ratio () and a tensor tilt (). It appears that
remains the same as in the local inflation in the leading slow-roll
approximation, while and get modified due to modification of the
tensor power spectrum. This class of models allows for any value of
with a modified consistency relation which can be fixed by future observations
of primordial -modes of the CMB polarization. This makes the UV complete
gravity a natural target for future CMB probes.Comment: 37 page
Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors
We consider the magnetic field dependence of the plasma resonance frequency
in pristine and in irradiated BiSrCaCuO crystals near . At
low magnetic fields we relate linear in field corrections to the plasma
frequency to the average distance between the pancake vortices in the
neighboring layers (wandering length). We calculate the wandering length in the
case of thermal wiggling of vortex lines, taking into account both Josephson
and magnetic interlayer coupling of pancakes. Analyzing experimental data, we
found that (i) the wandering length becomes comparable with the London
penetration depth near T and (ii) at small melting fields ( G) the
wandering length does not change much at the melting transition. This shows
existence of the line liquid phase in this field range. We also found that
pinning by columnar defects affects weakly the field dependence of the plasma
resonance frequency near .Comment: RevTex, 4 pages, 2 PS figures, Submitted to Phys. Rev.
Noncommutative Field Theories and (Super)String Field Theories
In this lecture notes we explain and discuss some ideas concerning
noncommutative geometry in general, as well as noncommutative field theories
and string field theories. We consider noncommutative quantum field theories
emphasizing an issue of their renormalizability and the UV/IR mixing. Sen's
conjectures on open string tachyon condensation and their application to the
D-brane physics have led to wide investigations of the covariant string field
theory proposed by Witten about 15 years ago. We review main ingredients of
cubic (super)string field theories using various formulations: functional,
operator, conformal and the half string formalisms. The main technical tools
that are used to study conjectured D-brane decay into closed string vacuum
through the tachyon condensation are presented. We describe also methods which
are used to study the cubic open string field theory around the tachyon vacuum:
construction of the sliver state, ``comma'' and matrix representations of
vertices.Comment: 160 pages, LaTeX, 29 EPS figures. Lectures given by I.Ya.Aref'eva at
the Swieca Summer School, Brazil, January 2001; Summer School in Modern
Mathematical Physics, Sokobanja, Yugoslavia, August 2001; Max Born Symposium,
Karpacz, Poland, September, 2001; Workshop "Noncommutative Geometry, Strings
and Renormalization", Leipzig, Germany, September 2001. Typos corrected,
references adde
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